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Oblique collisions of non-rotating spherical particles with a wall
Chára, Zdeněk ; Vlasák, Pavel ; Kysela, Bohuš
In the present paper non-rotating particle-wall collisions were experimentally investigated. By means of the PIV method a velocity field around falling spheres was analyzed. It was shown that the wake behind the particle which approached a bed in non-normal direction was asymmetrical and after the impact the wake passed the particle only along one side. This non-symmetrical velocity field resulted in additional forces which pushed the particle to an opposite direction than was the direction of the particle motion just after the impact.
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Saltation of sand in vicinity of cylindrical column
Kharlamova, Irina ; Kharlamov, Alexander ; Vlasák, Pavel
The paper presents a model of sand sediment transport in water stre am in vicinity of a high cylindrical col umn. It is assumed that an averaged turbulent flow is horizontally layered in vicinity of the cylinder. In ea ch layer the flow around the cylinder is modelled as a potential flow generated by a vertical dipole line. Flow in viscous sub-layer on the surface of the cylinder is neglected. The presented flow model is approximate; however it is simple for use. Trajectories of saltating particles near the cylinder were calculated. Further investigation of such flow will allow a determination of zones where solid particles will collide with the column. That might be useful for prevention of its damage or destruction
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Numerical model of saltation in open channel with rough bed
Kharlamova, Irina ; Vlasák, Pavel
The present contribution deals with a numerical modelling of a saltation of solid spherical particle in turbulent flow along rough bed in the open channel. The goal of the research is to obtain the dependences of average characteristics of particle saltation motion (as length and height of one particle jump) on flow parameters (which can be characterized e.g. by shear velocity and water depth) and bed roughness. The suggested dependences and calculated results are compared with analogical relationships introduced by other authors in literature.
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Sedimentation of dilute suspension in intermediate region
Vlasák, Pavel ; Chára, Zdeněk
The present paper describes the results of experimental investigation of the continuous sedimentation of a dilute model of fine-grained suspension in the intermediate region of settlement. The effects of particle size (glass beads of average diameter 150–850 μm), concentration, and inclination of the vessel axis on particle fall velocity were evaluated. It was confirmed that the local relative particle-liquid velocity has a practically constant value across the vessel cross-section. The settling pattern is strongly affected even by a very gentle slope of the vessel axis, which causes an asymmetrical absolute velocity profile and significant increase of the local concentration and absolute fall velocity of particles near the upward-facing wall of the vessel.
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Collision of a rotating spherical particle with flat wall in liquid
Lukerchenko, Nikolay ; Kvurt, Y. ; Chára, Zdeněk ; Vlasák, Pavel
The collision of the rotating spherical particle with a flat wall in liquid was studied experimentally. The glass and steel beads rotating in water and silicon oil were used. A high-speed video system recorded the bead motion before and after the collision. It was shown that the restitution coefficient depends not only on the Stokes number but also on the particle angular velocity; the restitution coefficient decreases with increasing of the rotational Reynolds number and decreasing of the Stokes number. These results can be useful in modelling of the two-phase flows near solid boundaries.
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Dependence of saltation parameters on bed roughness and bed porosity
Kharlamova, Irina ; Vlasák, Pavel
In numerical models of bed load transport a bed structure of channel could be described by two parameters, a size of bed particles and a standard deviation of normal distribution of bed particles in the vertical direction. The present paper deals with the effect of bed parameters on average length and height of one jump of saltating particle. A new formula was proposed for bed roughness based on size and standard deviation of the normal distribution of the bed particles. The dependences of length and height of the jump on the diameter of the saltating and bed particles were determined for different variation of vertical distribution of the bed particles.
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Motion of rotating spherical particles touching a wall
Chára, Zdeněk ; Vlasák, Pavel ; Keita, Ibrahima
The paper deals with an analysis of motion of rotating spherical particle in calm water, when the particle is in contact with a smooth, horizontal wall. The motion was visualized by a fast digital camera at 1000 frames/second. Based on software analysis the particle trajectories as well as rotational velocities were determined. Values of vertical, horizontal and rotational velocities were used as input parameters for numerical model and the results are compared with experimental data. Experiments were performed with glass particle of diameter 25 mm, initial values of rotational speeds varied from 500 to 3000 revolution per minute.
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Metody predikce měnových kurzů
Vlasák, Pavel ; Sedláček, Jiří (vedoucí práce) ; Čajka, Radek (oponent)
Cílem této práce je zkoumat závislost pohybu měnového kurzu na základních fundamentech ekonomiky v dlouhém období, jakož i testovat validitu vybraných indikátorů technické analýzy v krátkém období. Závislost měnového kurzu budu zkoumat za pomocí korelace a diskutovanými fundamenty budou hlavní makroekonomické ukazatele, jakými jsou vývoj produktu daných ekonomik (HDP), vývoj úrokových měr (pro studium jsem si zvolil krátkodobé úrokové míry) a vývoj peněžní báze (M2). K testování nejpoužívanějších indikátorů technické analýzy budu používat program Equis MetaStock Professional. Testovat budu dvě skupiny indikátorů, a sice trendové indikátory a oscilátory. Z první skupiny to budou zejména jednoduchý klouzavý průměr (SMA), exponenciální klouzavý průměr (EMA), vážený klouzavý průměr (WMA), triangulární klouzavý průměr (TMA) a MACD. Ze skupiny oscilátorů otestuji index relativní síly (RSI). Všechny tyto indikátory budou nejprve popsány v teoretické části této diplomové práce. Diplomová práce je rozdělena na dvě části -- teoretickou a praktickou. Teoretická část obsahuje dvě kapitoly, ve kterých se podrobněji věnuji možnosti analýzy mezinárodního devizového trhu Forex. První kapitola pojednává o fundamentální analýze. Zde se podrobněji budu věnovat možnosti determinace měnového kurzu za pomoci parity kupní síly, parity úrokových měr a nastíním také monetaristický přístup. Druhá kapitola se zabývá analýzou technickou. V praktické části, resp. ve třetí kapitole se následně věnuji využití obou metod v praxi s důrazem na technickou analýzu.
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Reologie vysokoviskózních potravinářských hmot
Štern, Petr ; Vlasák, Pavel
Reologické vlastnosti vysokoviskózních potravinářských hmot, především živočišného původu, výrazně ovlivňují jejich přípravu, homogenizaci a zpracování. U vybrané hmoty byl proveden komplexní reologický popis tokového chování při technologii jejího zpracování. Na základě zjištěných výsledků lze konstatovat, že výraznější vliv má viskoelasticita než viskozita.
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